Recently bone quality has been widely realized to be more predictive for risk of fragility fractures than bone mineral density (BMD). Our parent R01 human study (R01AR04054496) is to characterize defects in bone quality, independent of bone mass, that contributes to low-trauma fractures in 120 postmenopausal women (60 low-trauma fracturing women as cases and 60 healthy non-fracturing women matched for age and bone mass as controls). In the parent project, we mainly characterize human bone quality at the tissue and structural levels. However, we have not identified cellular biomarkers for bone quality so far. Circulating monocytes and B cells play critical roles in bone metabolism. Circulating monocytes are osteoclast precursors and sources of important signaling factors for osteoclastogenesis. Circulating B cells are involved in bone metabolism by secreting factors affecting osteoclastogenesis. Our preliminary functional genomic studies (mRNA and microRNA array studies) on human circulating monocytes and B cells have identified significant biomarkers underlying different BMD status. In response to a notice NOT-OD-09-058 (NIH announces the availability of recovery act funds for competitive revision applications), we propose this competitive revision project. The purpose of this revision project is to identify cellular biomarkers for human bone quality. We hypothesize that in postmenopausal women with osteopenia, differentially expressed genes in circulating monocytes and B cells from those who sustain low-trauma fractures and those who do not, provide biomarkers and/or mechanisms underlying variation in bone quality. To test the hypothesis, we have four Aims: 1) to extract total RNA and protein samples of circulating monocytes and B cells obtained from 50 postmenopausal women (25 cases and 25 controls) recruited from the parent project;2) to perform mRNA and microRNA array experiments for each RNA sample;3) to identify differentially expressed mRNAs and microRNAs and reveal potential target mRNAs for the differentially expressed microRNAs in each cell type;4) to validate the identified mRNAs and microRNAs markers by qRT- PCR and/or quantitative Western blot analysis at the protein level for each cell type in the same 50 subjects. This project will provide important biomarkers or genes for future basic research on the mechanisms that cause defects in bone quality, and are involved in the etiology of low-trauma fractures. Our study is translational in that it will develop methods for diagnosis, prevention and treatment of low-trauma fractures based on expression levels of relevant genes in human circulating monocytes and B cells. PUBLIC HEALTH RELEVANCE: The purpose of this human functional genomic study is to identify cellular biomarkers for human bone quality by taking advantage of the subjects recruited in our parent R01 study. This study is translational in that it will develop methods for diagnosis, prevention and treatment of low-trauma fractures based on expression levels of relevant genes in human circulating monocytes and B cells. This study will also provide important biomarkers or genes for future basic research on the mechanisms that cause defects in bone quality.